One of the most important and most difficult procedures in the process of a dentist making a crown or inlay is retracting the gingival tissues in order to be able to obtain an accurate impression of the margins of the crown or inlay which often lie in the sulcus, the narrow groove between the base of the tooth and the surrounding gingival tissues. In taking the impression for a crown or inlay, the dentist must record not only the margin but also the area beyond the margin so that the laboratory can assess the angle of emergence of the tooth from the root and can continue that angle in the contour of the crown or inlay for optimal smoothness of the margin and health of the tissues near the margin. The area beyond the margin often lies at the bottom of the sulcus, a location which is particularly narrow and difficult to record accurately with impression material.
In order to better record the area of the tooth bordering the bottom of the gingival sulcus with impression material, dentists have traditionally used a length of string, called retraction cord or thread, which they push down into the sulcus. The pressure of the cord in the sulcus on the tissues lining the sulcus as well as the hemostatic or astringent medicaments which may be carried by the cord aid in stopping bleeding, shrinking the tissues of the gingival sulcus, and mechanically widening the gingival sulcus in order to allow the dentist to more accurately record the base of the tooth bordered by the gingival sulcus.
U.S. Pat. Nos. 4,321,038; 4,522,593; 4,465,462; 4,871,311; 4,892,482; and 5,540,588 are examples of prior art relating to retraction of gingival tissues.
One disadvantage of all these prior art retraction cords, as these references are presently understood, is that they are supplied in lengths which have to be wrapped around a tooth and then mechanically seated into the base of the sulcus one area at a time with gingival packing instruments. The mechanical seating is time consuming and often traumatic to the tissues under the area of cord which is being packed as well as painful to the patient. The gingival packing instrument often slips off the cord and injures the gingival tissue. Furthermore, dentists frequently have difficulty getting the cord to stay down in the bottom of the sulcus after it has been packed down.
U.S. Pat. Nos. 5,358,403 and 5,480,303 to Groth illustrate devices for applying gingival retraction cord to a tooth. In the '403 patent, a loop of gingival retraction cord is formed with the free ends of the cord being held, as by a threaded plug, in the end of an elongated handle. The loop is placed around the tooth and the handle is twisted to, in turn, twist the gingival retraction cord and tighten the loop around the tooth. A packing tool is then used to urge the retraction cord into the base of the sulcus. In the '303 patent, the retraction cord has a loop extending outwardly from one end of a barrel shaped applicator, with the free ends of the retraction cord projecting outwardly from the opposite end of the applicator. The loop is placed around a tooth, with the free ends of the cord being pulled to reduce the size of the loop. The free end of the loop also passes through a lock which is pivoted to the barrel. The lock is twisted to engage the retraction cord at the location where the retraction cord passes from the barrel to the lock to prevent sliding of the retraction cord. Thereafter, the applicator is twisted so as to twist the loop of the retraction cord and tighten the loop against the tooth. A packing tool is then used to force or pack the gingival cord into the base of the sulcus.
These retraction cord applicators suffer from a number of disadvantages. For example, the pressure applied to the tooth and gingival tissues arising from twisting the cord is difficult to control. The difference between having the retraction cord in a closed but untightened state which applies no pressure around the circumference of the tooth and having the retraction cord in a twisted, tightened state to apply pressure around the circumference of the tooth may be only a millimeter or two. Further twisting the cord another millimeter or two may create too much pressure on the cord and against the gingival tissues. In addition, the applicators of these two Groth patents are relatively bulky, making them inconvenient to use during dental procedures. Moreover, packing tools which can traumatize the gums are still required to pack the retraction cord into the base of the sulcus.
Therefore, a need exists for an improved gingival retraction apparatus and method.